Identifying characteristics: The genus Rhododendron includes over 900 species. Species of the genus freely hybridize so an infinite number of cultivars are available. All azaleas are now classified under this genus, although some people still differentiate between "true rhododendrons" and azaleas: "True" rhododendrons are usually evergreen, have 10 or more stamens (azaleas typically have 5) and leaves are often scaly with small dots on the underside. Azalea leaves are generally hairy and the flowers are usually funnel-shaped, whereas "true" rhododendron flowers are bell-shaped. Some rhododendrons have some fall coloring in the leaves, and the large-leafed varieties are often subject to wind damage. The rhododendron in the Lagomarcino courtyard is R. carolinianum 'PJM,' named for Peter John Mezitt of Western Nurseries in Hopkinton, Massachusetts. Although a slow-grower, this plant exhibits a remarkable hardiness to the lower limits of zone 5, with the leaves undamaged by harsh winters. It is a sun-loving cultivar and withstands summer drought very well, as well as being reasonably wind-tolerant. Rarely setting seed, this cultivar is a dependable, prolific annual bloomer. Attaining a height and spread of 6 feet, this plant will lose its compactness and bloom less if too shaded. 'PJM' has alternate, evergreen leaves, 2 to 3 inches long. Dark green above and rust-colored and scaly beneath, the leaves turn purplish in colder climates in the winter. 'PJM' has pale, rose-purple flowers clustered at the shoot tips from early May into June. Most rhododendrons flower late spring and early summer with terminal clusters of 5 to 10 flowers. The fruit is a dehiscent capsule, best removed after the flowers have faded.
Similar species:
Ecology:
Rhododendrons are mostly native to the Northern Hemisphere, occurring in
the mountain ranges bordering Tibet, China, upper Burma and the eastern
US. In the US they are native to the Blue Ridge Mountains of the Carolinas
and Tennessee, where thin oak woodland with some evergreen cover typifies
their natural habitat. Cultivated most successfully in the eastern US and
the Pacific northwest, rhododendrons prefer moist, fertile, well-drained,
acid soil and grow best in a semi-shaded, sheltered position. Some alpine
species will grow in full sun and windy positions. Extremely sensitive to
salinity and high pH, rhododendrons will, however, withstand pollution.
Although good cultural practices reduce the susceptibility of rhododendrons
to pests and diseases, their cultivation is fraught with difficulty. Lace
bugs, canker, crown rot, borer, scale and nematodes are just some of the
problems. Fungal pathogens cause flower blight and extensive defoliation.
Uses:
Rhododendrons, planted en masse, provide more color than any other
flowering shrub. They are ideal for naturalistic, forest plantings and for
massed spring color effects, requiring no regular pruning. Besides particular
evergreen cultivars like 'PJM,' a number of deciduous "azalea"
cultivars of Rhododendron can also be grown in Iowa.
